Moz uses Google + and Facebook as their baselines so having images that are scaled to the reqs in those two would be the quickest solution. With Google you can bulk upload images in the dimensional range of 1000x1000 to 3000x3000 "We recommend adding photos that are larger than 1000 x 1000 pixels and smaller than 3000 x 3000 pixels." (https://support.google.com/business/answer/6031953) and then select what you want as a cover photo within Google+. See this guideline: https://support.google.com/business/answer/4791112.
And for Facebook a profile photo containing your company's logo must measure at least 180 by 180 pixels to meet Facebook's upload requirements. Once uploaded, the photo is resized to 160 by 160 pixels and placed within a 170 by 170 field, providing a small border between your profile photo and cover photo. Photos larger than 180 by 180 pixels are scaled down to fit within the profile template. (from: http://smallbusiness.chron.com/size-facebook-business-logos-57290.html)